On space missions beyond low Earth orbit, such as on missions to Earth's moon, to Mars, or elsewhere, Earth's atmosphere and magnetosphere are not available to protect the crew of the mission from sources of ionizing radiation. Such radiation may include the solar wind, cosmic radiation, solar flares or other solar particle events, and other radiation sources or events. Effects of exposure to radiation from a major solar event or other radiation event could place the crew of a space mission at significant risk for acute radiation sickness. Such acute exposure could impact crew health and performance during their mission, endangering completion of the mission and the safe return of the crew to Earth. Protracted exposure to lower levels of radiation (e.g., the solar wind or cosmic radiation) may increase the likelihood of cancer or other radiation-induced disorders for crew members many years after the completion of their mission.
Shielding the entire habitable area or cabin of a spacecraft is not currently feasible. Effectively shielding an entire crew module (such as that of the Orion spacecraft) would require very large quantities of shielding material. Delivering such a quantity of shielding material to space would entail much added expense and time, or would require use of a lunch vehicle that is larger than any that are expected to be available in the foreseeable future. Addition of the extra mass without a corresponding increase in propulsion power could increase travel time to a destination, increasing exposure to the radiation. In addition, such cabin shielding would not provide any shielding for an astronauts during and extravehicular activities.
Drugs are under development to mimic or enhance the body's natural capacity to repair damage caused by radiation. Although there has been some progress in development of drugs for countering the effects of terrestrial ionizing radiation, such as gamma radiation, very little progress has been made towards countering the effects of the type of radiation (high-energy and massive charged particles) that is encountered during space travel. If such a drug were to be developed, it would probably have to be administered several hours before exposure. However, solar particle events cannot currently be forecast in advance. Furthermore, pharmaceuticals have been found to become unstable during space travel, possibly due to protracted exposure to radiation and vibration.
Magnetic deflection and electrostatic repulsion has been considered for reducing exposure to radiation in space. However, a compact system may require magnetic field strength as large as 10 tesla to 20 tesla. Such high fields have been known to produce headaches and migraines in magnetic resonance imaging patients, and long-duration exposure to such fields has not been studied. Devices to produce such a magnetic field may add thousands of kilograms to the mass of the spacecraft.
Personal shielding that is worn on an astronaut's or other user's body enables placement of the shielding adjacent to the area of coverage. The solid angle of coverage is thus maximized, thus enabling a reduction (relative to shielding of an entire cabin or spacecraft) in the mass of shielding that is required to provide equivalent protection.